An RF power splitter/combiner is a passive circuit that has a major port and two or more minor ports interconnected such that RF power applied to the major port is apportioned into (usually equal) amounts that are then available at the minor ports (assuming that they are properly terminated). Conversely, power applied to the minor ports is summed and made available as a combined amount at the major port.
Some devices of this class are fabricated of resistors, connectors and a housing. They resemble minimum loss pads and afford excellent flatness over wide bandwidths (DC to 18, 26.5 or 50 GHz). Resistor types offer excellent SWR and minimal disturbance (change in the ratio) to remaining ports when the impedance terminating one port is not ideal. Unfortunately, they also dissipate power internally, and more than one of these expensive laboratory devices has turned into smoke when someone innocently attached a 50 .OMEGA. splitter rated at +27 dbm max onto the antenna of a five watt transceiver and then keyed the mike.
More rugged are the reactive or "transformer" type, often made of sections of coaxial transmission lines that are cleverly interconnected to variously place the sections in series and parallel. They are not as flat, have definite limits on bandwidth, and have division ratios that are sensitive to mismatch. However, they are often considerably less expensive, and since they do not have resistors in series with the path of the power, do not go up in smoke as readily as that other kind. Properly terminated, they can also have excellent isolation between the minor ports. This makes the reactive or transformer type of splitter well suited for use in a wide variety of commercial settings, including some laboratory ones where isolation is prized over issues of extreme bandwidth and flatness.
The ANZAC DS-409-4 is one such reactive or transformer type of power splitter. It has one major port and four minor ports, and is usable from 10 MHz to 2000 MHz at levels up to five watts. Internally, the ANZAC DS-409-4 has four short (approx. 1.25") pieces of hard line (tiny semi rigid coax, 0.047" outside diameter), two of which carry ferrite sleeves over their outer shields.
Unfortunately, it is not of simple construction. Of the four pieces of hard line, two are angled into a common point at an enclosed angle of about 100.degree.. Each does a 180.degree. U turn at its other end. The other two pieces are shaped as broad and shallow U's or arches, and cross over each other at one end where they otherwise meet at about 100.degree., as for the other pair. None of the four pieces of hard line is straight. (That is, has an unbent outer shield; it is not here an issue for a center conductor extending slightly beyond the end of the shield to bend 90.degree. to reach its destination.) The unit includes a printed circuit board having two rectangular slots; these allow the two pieces of hard line having the ferrites to originate on one side of the board, pass through the slots, and terminate on the other side of the printed circuit board. This gives rise to two additional right angle bends to enter the board perpendicularly, just after the U turns. All in all, assembly of such a splitter is not an easy task, and probably no two of them are quite alike, since instead of simply placing preformed parts in place and soldering them, each piece of hard line appears to have been individually "wrestled" into place. It further appears from a cross coupling in the schematic that, given the 100.degree. angle, some of the pieces of hard line must either cross each other, or pass from one side of the board to the other. In the ANZAC part they do both. (Amendatory note: Since this Application was filed it came to light that the business interests of ANZAC, formerly of Buffington, Mass., have been acquired by MA/COM, with a manufacturing site presently located in Amesbury, Mass.)
It would be desirable if a four way RF power splitter/combiner could be more easily fabricated.